Neural development: How the brain gets organised and efficient
Synaptogenesis is the formation of new synaptic connections between neurons, most active in early childhood.
Synaptic pruning eliminates unused neural connections, allowing the brain to specialise and function more efficiently.
Myelination insulates axons with myelin sheaths, speeding up neural transmission from childhood through adolescence.
Common Mistake
Critical periods have hard deadlines after which recovery is difficult (e.g. binocular vision development).
Sensitive periods are optimal windows for development but learning can still occur outside them (e.g. language acquisition).
Students often conflate these terms; use them precisely in exam answers.
Critical and sensitive periods: Windows for optimal development
Critical periods are narrow developmental windows with hard cutoffs; missing them prevents normal development (binocular vision, language phoneme discrimination).
Sensitive periods are extended optimal windows when the brain is most responsive; development continues more slowly outside them (first language acquisition, attachment formation).
Note
Environmental enrichment during sensitive periods has lasting effects on neural architecture and cognitive capacity.
Deprivation during critical periods can cause irreversible deficits; deprivation during sensitive periods causes delays that may partially recover with intervention.
Prefrontal cortex development: Why adolescents take risks
The prefrontal cortex continues developing until the mid-20s, governing executive functions: planning, impulse control, and risk assessment.
The limbic system (emotion and reward centres) matures earlier in adolescence.
This asynchrony explains adolescent risk-taking, sensation-seeking, and emotional impulsivity: reward sensitivity outpaces self-control.
Example
An adolescent might know skateboarding without a helmet is dangerous (prefrontal assessment) but still do it for peer approval (limbic reward activation).
Grey and white matter changes: Evidence from brain imaging
Grey matter (neuron cell bodies and synapses) peaks during early adolescence, then decreases via pruning.
White matter (myelinated axons) increases steadily through adolescence, improving communication between brain regions.
Giedd et al. (1999) used longitudinal MRI to document this pattern: grey matter peaks then synaptic pruning reduces it, while myelination increases white matter, enhancing neural efficiency.
Theory of Knowledge
Knowledge: Grey and white matter changes follow predictable developmental patterns.
Methodology: Giedd's longitudinal design strengthens causal claims about development compared to cross-sectional studies.
Perspective: Biological evidence grounds cognitive and behavioural changes in neural architecture.
Neural plasticity: How experience reshapes the brain
Neural plasticity is the ability of the brain to reorganise itself and form new neural pathways in response to experience and learning.
Highest in early childhood; declines gradually but remains throughout adulthood, enabling recovery from brain injury and learning of new skills.
Analogy
Like a river changing course, the developing brain redirects resources (synapses, myelination) based on what's needed most; unused pathways fade.
Exam technique: Linking brain development to behaviour
Exam technique
Explicitly mention asynchronous prefrontal-limbic development when explaining adolescent risk-taking; this is the biological mechanism examiners expect.
Reference Giedd's longitudinal MRI findings when discussing brain structural changes across development.
Link synaptic pruning to improved cognitive efficiency and specialisation, not as deficit.
Connect neural plasticity to importance of early intervention and environmental enrichment for optimal outcomes.
Active recall
Define and distinguish critical periods from sensitive periods with an example of each.
Explain how asynchronous prefrontal and limbic development creates vulnerability to risk-taking in adolescence.
Describe the pattern of grey and white matter changes shown in Giedd et al.'s study and what this reveals about neural efficiency.
Analyse how environmental enrichment during sensitive periods leads to lasting brain changes via synaptic density and myelination.
Evaluate how neural plasticity supports both recovery from injury and the impact of early intervention programmes.
